Concrete is a common material for use in the construction of larger buildings because the concrete is relatively inexpensive and has good compressive strength. Buildings such as multilevel apartment buildings, office buildings and the like are designed to support their own weight plus that of expected inhabitants and furnishings. Concrete materials have excellent vertical compression properties, thus are used in such structures.
Many different techniques have been used to reinforce concrete. One common method for reinforcing concrete includes the use of a reinforcing sheet made of reinforcing fibers, such as carbon fibers, aramid fibers, glass fibers, or the like, that are attached on the surface of a concrete surface. The reinforcing sheet is arranged and attached along an outer surface of the concrete surface to reinforce the concrete against bending stresses applied thereto. The reinforcing sheet is generally attached to the concrete by an adhesive. However, when the reinforcing sheet is merely adhesively attached to the concrete, the edges of the reinforcing sheet or the entire reinforced sheet can become delaminated or debonded from the concrete. As such, the edges of the reinforcing sheet are typically joined to the concrete by use of an anchor that is hammered and joined into the concrete. However, hammering the anchor to join the edges of the reinforcing sheet requires a great deal of time and the anchors or the fitting members generally protrude from the surface of the concrete which is aesthetically displeasing and/or creates other problems such as when facing panels are to be connected to the concrete.
Another prior art method for reinforcing concrete is to secure a reinforcing sheet to the concrete by forming holes in the concrete and passing the reinforcing sheet through the holes and subsequently filling the holes with a resin material, a mortar, or the like. This method can be very time consuming and labor intensive. Also, the drilling of holes through the concrete can result in damage to the concrete.
Another prior art method to reinforce concrete is by coating the concrete surface and attaching a steel plate to the coated concrete surface. However, steel plates are heavy and difficult to install. The weight of the steel plate can also create weight issues in the building. Also, the reinforced concrete becomes substantially thicker as compared to the original structure when steel plates are attached to the concrete, thereby reducing room space.
Two prior art methods have been developed to overcome these past problems associated with reinforcing concrete and are disclosed in U.S. Pat. No. 6,330,776 and U.S. Pat. No. 7,574,840, both of which are fully incorporated herein by reference. The '776 patent discloses the use of an anchor that is formed of a plurality of reinforcing fibers such as carbon fibers, aramid fibers, glass fibers, and the like. A portion of the anchor is bundled in the longitudinal direction and inserted into a hole in a concrete structure, and the remaining portion of the anchor that is not bundled, is spread or splayed on the surface of the concrete structure. This type of anchor is known as a Splay anchor. A reinforcing member in the form of a plate or sheet is thereafter connected to the surface of the concrete structure and to the portion of the anchor spread or splayed on the surface of the concrete structure. A bonding material is inserted into the hole containing the bundled portion of the anchor so as to secure the anchor in the hole in the concrete structure. A bonding agent is also used to secure the reinforcing member of the portion of the anchor spread or splayed on the surface of the concrete structure.
The '840 patent also discloses the use of an anchor that is formed of a plurality of reinforcing fibers such as carbon fibers, aramid fibers, glass fibers, and the like. The '840 patent discloses that the middle portion of the anchor is bundled and is designed to be inserted into a hole in a concrete structure and the remaining portion of the two ends of the anchor that is not bundled, is spread or splayed on the surface of the concrete structure or another concrete structure. A bonding material is inserted into the hole containing the bundled portion of the anchor so as to secure the anchor in the hole in the concrete structure. A bonding agent is also used to secure the portion of the anchor spread or splayed on the surface of the concrete structure, and to secure a reinforcing member on the concrete structure and to the anchor.
The purpose of the anchors disclosed in the '776 patent and the '840 patent is to ensure that the reinforcement strip used to reinforce the concrete reaches its maximum capacity. As such, the problem the anchors are meant to deal with is to maintain the reinforcement strip and concrete structure together long enough such that the reinforcement strip can reach its maximum capacity. The bond between the reinforcement strip and the concrete surface is much weaker than the strength of the reinforcement strip. When a concrete beam or column begins to bend, such bending only accelerates the debonding of the reinforcement strip from the concrete surface, thus resulting in the reinforcement strip peeling off of the concrete surface. The anchors are not designed to prevent the reinforcement strip from debonding from the concrete. Additional prior art anchors are disclosed in U.S. Pat. No. 6,389,775 and U.S. Pat. No. 7,207,149, and, Burr, Alan C. “Recent Developments in the Use of FRP Anchors and Masonry Wall Strengthening Techniques.” The Structural Engineer (2004): 20-21; Kim, S. J., and S. T. Smith. “Behavior of Handmade FRP Anchors under Tensile Load in Uncracked Concrete.” Advances in Structural Engineering 12.6 (2009): 845-65; Niemitz, Carl W., Ryan James, and Sergio F. Breno. “Experimental Behavior of Carbon Fiber-Reinforced Polymer, CFRP . . . Sheets Attached to Concrete Surfaces Using CFRP Anchors.” Journal of Composites for Construction 14.2 (2010): 185-94; Özdemir, Gökhan, and :. Akyüz, U{umlaut over (g)}urhan. Supervisor. Mechanical Properties of CFRP Anchorages. Thesis. Middle East Technical University, 2005, Pham, Le Tuan. Development of a Quality Control Test for Carbon Fiber Reinforced Polymer Anchors. Thesis. University of Texas at Austin, 2009, all of which are fully incorporated herein by reference.
Although the prior art methods for reinforcing concrete disclosed in the '776 patent and the '840 patent are effective in strengthening the concrete, the anchors fail long before the reinforcement strip can reach its maximum capacity. As such, there remains a continued need to simplify the reinforcing installation process and to improve the strength of the reinforced concrete.